Engineers and other decision-making agents utilize data about the materials of fabrication for load bearing structures to determine their durability, reliability and the overall safety. The data can be from a number of sources including the original manufacturing specifications, from manufacturing quality control, or from measurements done after the fact as part of condition assessment. Nondestructive testing (NDT) methods are appealing because they allow for estimating the characteristics and properties of assemblies and structures without damaging or jeopardizing the function of the structure during testing.
Nondestructive testing during condition assessment on existing structures in the field is very important to safety and the protection of the environment. We have a large inventory of existing infrastructures that may have changed from the time they were originally manufactured as well as existing infrastructures that would not meet the current standards of design and fabrication. One goal with condition assessment is to minimize the risk of a catastrophic event such as the break of a large oil or gas pipeline, the collapse of a bridge or the failure of a large pressure vessel. These events still occur too frequently in our society.
Nondestructive testing can be used to evaluate, among others, the existence and size of cracks, changes in material thickness for corrosion, and the properties of the materials. Properties of the materials that can be of interest include the chemistry, mechanical properties and the cracking resistance under the service environment and/or the cyclic loads.
Nondestructive techniques for mechanical properties have proven capable of measuring the hardness, strength, and ductility of a material by utilizing a form of indentation referred to as frictional sliding, whereby a stylus is indented into a substrate and displaced laterally across the substrate surface. To determine the material properties, the stylus reaction forces and its relative displacement are monitored throughout the test. While the mechanisms of this process are well studied, implementation was previously difficult due to sample surface curvature, as well as situations in field environments during which a sample could not be removed and the material had to be tested in-situ (i.e., bridge, pipelines, sub-frames).
Recent industrial innovations by Bellemare et al., as outlined in U.S. Pat. No. 9,933,346, have enabled the utilization of these contact mechanics techniques in field conditions. One of the limitations in the apparatus described in U.S. Pat. No. 9,933,346, however, is the mechanical space required for implementing multiple styluses within one apparatus, a technique that has proven value in testing accuracy. Each stylus, which remains independent from the others due to the nature of the test, requires independent load application, alignment, and monitoring. As each of the components requires significant space, the size of the device can become unwieldy.